Numerous types of fluid dispensing apparatuses exist.
For example, one type of fluid dispensing apparatus currently in widespread use is a positive displacement filler, which for fluid dispensation relies directly upon mechanical means that physically contact and positively displace fluid. Positive displacement fillers often use a piston and cylinder arrangement, wherein the backward movement of the piston draws fluid into a cylinder through an inlet and the forward movement of the piston expels the fluid through an outlet. Alternatively, a rotary pump can be used to displace fluid. Positive displacement pumps can operate at relatively high speeds, filling as many as six hundred bottles per minute, and can achieve levels of accuracy up to about ±0.5%.
A disadvantage of positive displacement fillers is that fluid, during operation, comes into contact with moving parts. As the moving parts wear, particulate matter can enter the fluid causing particulate contamination. If severe enough, particulate contamination can render the dispensed fluid product unusable.
Another disadvantage with positive displacement fillers involves the difficulty in cleaning and sterilizing its wet moving parts. In positive displacement pumps, the critical tolerances between pads, such as the piston and cylinder, precludes effective in situ cleaning. Thus, the user must disassemble the apparatus for cleaning and sterilization. This process is not only time consuming, but may result in biological contamination of the pads when handled by the mechanic during reassembly.
Another type of fluid dispensing apparatus is the time/pressure filler, which in operation generally relies upon a fluid reservoir maintained under relatively constant pressure. The fluid is dispensed from the reservoir through a compressible line. Fluid flow is shut off by a pinch type valve which squeezes and collapses the discharge line. A pre-determined volume of fluid is dispensed by opening the discharge line for a pre-determined period of time and then closing the line. If the pressure within the fluid reservoir is maintained constant, an equal amount of fluid should be dispensed each time the cycle is repeated. However, it has been observed that time/pressure fillers often do not work as well in practice as they do in theory.
Another type of fluid dispensing apparatus is a volumetric fluid dispensing apparatus. A volumetric dispensing apparatus—such as shown in U.S. Pat. No. 5,090,594—measures a predetermined volume of fluid in a measuring cup or fill tube, then subsequently dispenses it into a receptacle. Volumetric fillers, although slower than positive displacement fillers, are accurate and avoid the problems of microbial and particulate contamination. However, volumetric fillers, like time/pressure fillers, depend on a relatively constant pressure. Pressure irregularities, such as may be occasioned upon use of clarification filters, can lead to inaccurate filing.
Another type of fluid dispensing apparatus is described in U.S. Pat. No. 5,480,063, issued to Keyes et al. on Jan. 2, 1996. Keyes et al. describe an apparatus having no moving parts in contact with the fluid being dispensed. The apparatus includes a fluid reservoir and a fill tube communicatively connected thereto. The fill tube forms a closed circuit with the fluid reservoir. In operation, fluid is transferred from the reservoir into the fill tube. When the fluid level in the fill tube reaches a predetermined height, fluid transfer is terminated, and fluid dispensed from the fill tube into a container.
The fluid dispensing apparatus of Keyes et al. provides advantages not found in the other types of fluid dispensing apparatuses, and accordingly, has become of late an area of considerable technical and commercial interest. Regardless, current embodiments—though they provide good results—can be improved. In particular, the current means used to monitor fluid levels therein—i.e., optical sensors—are effected by the optical properties of the fluid and on the mechanical assemblages that move the sensors correspondent with the rise and fall of fluid meniscuses. The level of a viscous fluid, which tend to coat interior wall surfaces, can be difficult to determine with precision. Further, the use of said mechanical assemblages (including, for example, a stepper motor) can generate particles at levels unacceptable for certain sterile applications.